[ELI5] what are the different ways of making glasses?

Question

I wear a very negative prescription. My recent glasses got made with a very negative sphere and a positive axis. My ones before has both of them negative. How does that work?

In: 1

Answer 1

There’s two ways to write a prescription either in plus cylinder or minus cylinder. Typically optometrists work in minus cylinder and ophthalmology works in plus cylinder. You can transpose minus cylinder to plus cylinder by combining the sphere and the cylinder and adjusting the axis by 90 degrees. So -4.00 -2.00×90 would be the same RX as -6.00 +2.00 ×180